Method for preventing adhesion and growth of barnacles



Dec. 23, 1958 w. M. BRUNER 2,865,702

METHOD FOR PREVENTING ADHESION AND GROWTH on BARNACLES Filed April so,1956 WALTER MARTIN BRUNER United States Patent METHOD FOR PREVENTINGADHESION AND GROWTH OF BARNACLES Walter Martin Bruner, Wilmington, Del.,assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, acorporation of Delaware Application April 30, 1956, Serial No. 581,412

1 Claim. (Cl. 212) This invention relates to inhibiting the growth ofbarnacles on marine structures.

Heretofore it has been known that polytetrafluoroethylene adheres verypoorly, or not at all, to other surfaces. Coating compositionscontaining polytetrafluoroethylene in colloidal form have, however, beendeveloped, and these coating compositions adhere well to varioussurfaces. For example, such coating compositions have been applied tomarine structures with excellent protective effects. However, it hasbeen observed that the coatings thus produced do not suppress adherenceand growth of barnacles on the structures thus coated. Experimentsperformed at the Mare Island Naval Shipyard, Vallejo, California(reported in Department of Navy, Bureau of Ships publication entitledProtective Coatings for Shipbottoms, NS-O61-002, August 15, 1955) led tothe conclusion that polytetrafluoroethylene coatings (applied in theform of dispersions) exhibited no antifouling (antibarnacle) property.Marine growth accumulated rapidly and abundantly on the surface thustreated, just as it did on other non-toxic surfaces such as glass, wood,mild steel, and porcelain.

The present invention is based upon the discovery that, in sharpcontrasts with the results heretofore reported, suppression of barnaclegrowth does occur if the polytetrafiuoroethylene is applied to thesurface in the form of a substantially impervious sheet or film, asdistinguished from a coating obtained by applying apolytetrafluoroethylene dispersion or other coating compositioncontaining colloidal polytetrafluoroethylene (Ikeda, U. S. P. 2,592,147,issued April 2, 1952, and Berry U. S. P. 2,478,229, issued August 9,1949).

Polytetrafiuoroethylene sheets which are substantially impervious tofluids can be made by methods now well known in the art (Llewellyn, U.S. P. 2,586,357), issued February 19, 1952. They can be obtained in anydesired thickness. In specific embodiments, the sheets are relativelythicker than ordinary coatings, and suitably have a thickness of about 2to 60 mils.

Ships having hulls clad with polytetrafluoroethylene sheets havenumerous incidental advantages, apart from freedom from barnacle growth.The friction between such polytetrafluoroethylene-clad surface and wateris at a low minimum, and such surfaces are relatively ageresistant.

In preparing the structures used in the practice of the presentinvention, any method for bonding the polytetrafluoroethylene to thebase surface may be employed. An outstanding method for producingadhesion of polytetrafluoroethylene is that described in Chemical Week,78, 90, February 11, 1956.

2,865,702 Patented Dec. 23, 1958 ICC The invention is illustratedfurther by means of the following examples.

Example 1 A smooth polytetrafluoroethylene impermeable sheet (60 milsthick) was attached to a steel plate which was nailed to the bottom of aboat, and the resulting structure, which was initially clean, wasmaintained for six weeks under barnacle-growth conditions near otherbottom surfaces in the Sassafras River in Maryland. Barnacle growth wasrapid on the rest of the boat bottom and on the other surfaces, butthere was a complete absence of such growth on thepolytetrafluoroethylene surface. The drawing attached hereto is based ona photograph of the boat bottom after the test was completed.

Example 2 A sheet of impermeable polytetrafluoroethylene, 10 mils thick,was cemented to the bottom of a wooden boat by means of theabove-mentioned process, namely by roughening both surfaces of the sheetwith a sodium-ammonia solution, followed by adhesively bonding the sheetto the boat bottom by means of a commercial epoxy resin adhesive. Theadhesive bond was cured by overlaying the polytetrafluoroethylene sheetwith an aluminum foil and applying a hot iron to the aluminum overlay.The latter was then removed. One half of the exposed cementable surfacewas subjected to abrasion to remove the cementable skin produced by thesodium-ammonia. The other half of the exposed cementable surface was notsubjected to abrasion. The resulting structure was maintained for fourmonths under barnacle-growth conditions. Barnacle growth was prolific onthe surface outside of the patch and along the edges of the patch.Within the patch itself, growth was only about one-tenth as dense as onthe unabraded cementable half, and about one-thirtieth as great on thehalf from which the cementable skin had been removed by abrasion.

These examples are illustrative only, and it is to be understood thatnumerous other illustrations could be given without departing from thespirit and scope of the invention. Example 2 is of special interest inthat it shows that when the exposed surface had been renderedcementable, it did not completely protect against barnacle growth (cf.the complete protection provided in Example 1), and that the surfacefrom which the cementable coating had been removed by abrasion also didnot completely protect against growth, although in each instance growthwas considerably inhibited. Smoothness of exterior sur- 7 face, coupledwith absence of cementability, are there- No references cited.

